Gallium nitride (GaN) and other wide band-gap nitride III based direct transitional semiconductor materials are advantageously utilized in certain electronic devices due to their superior physical prosperities over silicon-based devices. For example, GaN and AlGaN/GaN transistors are commonly used in high-speed switching and high-power applications due to the high electron mobility, high breakdown voltage, and high saturation electron velocity characteristics offered by GaN-based materials and device structures.
GaN and AlGaN/GaN integrated circuit (IC) devices are typically prepared by epitaxial growth of a semi-insulating (highly-resistive) GaN buffer layer on a substrate material such as Sapphire, Silicon Carbide, single crystal GaN, Si and so on. For high voltage operations, the IC device is required to have a high breakdown voltage VBR with minimal leakage current through the GaN buffer layer. One source of leakage current is the unintentionally doping (UID) by residual donors such as oxygen in the GaN buffer layer. For example, oxygen may be unintentionally introduced into the GaN buffer layer as a result of surface contamination during frontend and backend fabrication processing steps. In addition, charge build-up (either positive or negative) may occur at the interfaces as a result of the piezoelectric nature of GaN and multiple dielectric depositions commonly performed during passivation. This charge build-up can adversely impact the voltage-current characteristics and frequency response of the IC device.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.